<Abstrate>

Three groups of Cu bicrystals with their component grains sharing one common

{111} slip plane were cyclically deformed. By careful design on the loading direction,

coplanar slip systems operated in the two component grains. Three kinds of grain

boundaries (GBs): a low angle grain boundary (LAGB), a high angle grain boundary

(HAGB) and an incoherent twin boundary (ITB), were all impinged by coplanar slip

bands (SBs) on both sides. Nonetheless, the three kinds of GBs showed different

fatigue cracking behaviors: the fatigue cracks nucleated along the HAGB earlier

than along the SBs which produced cracks earlier than both the LAGB and the ITB.

It is found that the slip vectors of the two component grains deviate from each other

to different degrees for the three kinds of GBs. Lattice dislocations tend to pile up at

the HAGB due to the large difference between the slip vectors, while lattice

dislocations tend to pass through the LAGB and the ITB ascribed to the small

differences between the slip vectors. High ability of dislocation transmission can

generate good strain compatibility and low stress concentration near the GBs so as to

increase the intergranular fatigue cracking resistance. In addition, lattice dislocation

transmission and boundary dislocation motion can induce migration of LAGB and ITB

which could improve the intergranular fatigue cracking resistance by consuming part of

plastic work done by the cyclic loading. Thus, fatigue cracking resistance of GBs with

impingement of coplanar SBs can be improved by increasing the penetrability

and mobility of the GBs.
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